1. Field of the Invention
The invention concerns an absolute interferometric measuring process, in particular for absolute distance measurements, employing a laser which can be tuned without mode-jumping in at least one wavelength range and a measuring interferometer which is subjected to the laser beam, whereby at least one of the interferometer arms is configured as a variable measuring line, and a laser interferometer configuration suitable for the measuring process, incorporating a laser which is tunable without mode-jumping in a certain wavelength range and a measuring interferometer, on which at least one interferometer arm forms the measuring line, whereby a beam-splitter and two reflectors are provided for the purpose of generating at least two mutually interfering component beams, and with a photodetector provided on the interferometer arm for the purpose of detecting the interference signal, further with a counter or electronic counting device for the purpose of measuring the phase change and a control device for the laser wavelength.
2. Description of the Prior Art
A device for measuring the distance of an object via the use of a laser beam, consisting of a measuring interferometer and a reference interferometer, is known from DE-PS 36 08 075. Both interferometers are supplied with the beam from the same laser. By means of frequency modulation of the laser beam, a so-called reference beat wave is generated from each 2 mutually interfering component beams, whereby the respective numbers of waves in the measuring beat wave and the reference beat wave are determined using a measuring device, and the measuring line is determined on the basis of the ratio between the numbers of these waves and the known reference distance. With this process, a measuring device begins counting the waves in the reference beat wave at the same point in time at which it begins to count the waves in the measuring beat wave. Consequently, the number of waves in the reference beat wave is not generally integral. The process takes account of this situation by virtue of the fact that the measuring device is designed in such a manner as to enable the number of waves in the reference beat signal to be determined with a level of precision which is more accurate than the decimal point.
On the basis of these specifications, the phase of the reference beat wave has a maximum resolution of approximately 1/10 of the total wavelength. This resolution falls far short of the resolutions attainable with other methods, however.
A laser interferometer is also known from DE-PS 34 04 963 whereby, in addition to the actual measuring interferometer, an additional, so-called control interferometer is employed to control the air wavelength. This control interferometer serves to compensate any disturbances of the air wavelength which may occur within the measuring line of the measuring interferometer in the course of a measuring operation.